The field of the invention is sensors for determining the linear position of an object and, more particularly, linear resolvers.
Linear resolvers have generally been known and used in the prior art. Such prior art linear resolvers are analogous to their rotary counterparts, except that the excitation and secondary windings are laid out flat, comprising primary and secondary coils adapted for relative linear motion. An example of such a system is described in U.S. Pat. No. 4,705,971. Other types of linear resolvers utilize a movable slug or magnetically permeable actuator to alter the coupling from primary to secondary.
One drawback of prior linear resolvers is that they are unable to directly sense the position of an object. Instead, the object to be sensed must be mechanically linked to the linear resolver mechanism. Some systems are known for sensing the presence of a magnetically permeable object by using magnetic coupling through the object to establish its presence or absence, or even an approximate position, but such systems are unable to provide the precise position information available from a resolver.
Another drawback of prior linear resolvers is that they are able to determine the position of only one object at a time, e.g. the object coupled to the actuator. In the case of prior magnetic sensing devices too, only one object can be sensed at a time; the presence of multiple objects would result in erroneous readings.